Climate

Melting Glaciers Are Causing the Ocean Floor to Sink

The added weight from melting land ice has depressed the seafloor about 0.005 inches annually between 1993 and 2014, demonstrating the large-scale impacts of climate change.

An iceberg broken off from a melting glacier floats in Lake Argentino, which holds runoff water from the Southern Patagonian Ice Field, the third largest ice field in the world, on November 28, 2015 in Santa Cruz Province, Argentina. | Mario Tama/Getty Images
An iceberg broken off from a melting glacier floats in Lake Argentino, which holds runoff water from the Southern Patagonian Ice Field, the third largest ice field in the world, on November 28, 2015 in Santa Cruz Province, Argentina. | Mario Tama/Getty Images

With solid data showing that the oceans have been rising slowly but surely for more than a century — more than 3 inches since 1993 alone, according to NASA satellite readings — scientists have long been sounding alarm bells about melting glaciers, coastal flooding, and other problems.

Now researchers in the Netherlands and Australia believe those satellites might have overlooked a small but potentially significant amount of water in the rising seas due to the compression that occurs as more water presses down on the ocean floor.

Writing in the journal Geophysical Research Letters, the scientists claimed the weight of the ocean has depressed the seafloor by around 0.005 inches annually from the period they studied between 1993 and 2014, or a little more than a tenth of an inch in total. That means scientists and others have likely missed around 4 percent of the total additional volume of water that has flowed into the oceans from melting glaciers and other sources due to climate change, they argued.

“The Earth is not rigid. The whole Earth is more like elastic liquid,” study co-author Thomas Frederikse, a sea level scientist and Ph.D. candidate at Delft University of Technology, told Seeker. “A lot of people don’t realize that.”

Linear trends and accompanying 1σ confidence intervals resulting from ice mass and LWS changes over 1993–2014 in (a) solid Earth deformation over the oceans, (b) relative sea level, and (c) geocentric sea level. Note that geocentric sea level change is equivalent to the sum of relative sea level and ocean bottom deformation change. The blue line depicts the line where local sea level change is equal to the ocean mean sea level trend, whose value is written in blue under each map. | Geophysical Research Letters

The findings don’t necessarily alter expectations about the looming threats of climate change. But they underscore how greenhouse gas emissions are changing the face of the Earth. “Because of climate change, human beings are deforming our planet,” said Frederikse.

Satellites measure sea levels by comparing their position in orbit to the distance from the ocean surface. But they use the center of the Earth as their reference point. They wouldn’t necessarily see a change in the volume of the oceans as they grew deeper, the researchers wrote.

The team received support from the Netherlands Organization for Scientific Research, the Australian Research Council and the Australian Research Council Special Research Initiative for Antarctic Gateway Partnership and Discovery Project.

Scientists knew that the seabed contracts under high tides and expands during low tides, so the findings weren’t a surprise, said Don Chambers, a professor in the College of Marine Science at the University of South Florida who was not involved in Frederikse’s study. Chambers also noted that the Intergovernmental Panel on Climate Change and others wouldn’t change their forecasts of the effects of climate change due to the findings.

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But the study nonetheless was a valuable advance in calculating the challenge that climate change poses. “That doesn’t seem like a lot,” Chambers, referring to the 0.005 inches per year, told Seeker. “But that is a substantial change in the seafloor. It does show the large forces at play here when you are moving water around because water is pretty heavy.”

Frederikse echoed those thoughts. He and his colleagues in his field refer to a “sea-level budget,” or an account of the rising and falling of the oceans that is analogous to tallying assets and liabilities on a balance sheet. In the same way accurate accounting is essential to running a business, knowing how the seas are rising is vital to figuring out how to deal with the problem.

“It gives us more confidence that because we understand the past, we can forecast the future better,” said Frederikse. “We want to do this bookkeeping. If you go to a place like New York and we see sea levels rising, we want to know why.”